The invention is directed to a digital electronic system for producing mixture tones simulative of mixture tones produced in a pipe organ.
In a pipe organ, the term "mixture" refers to a particular type of compound stop. A compound stop, when drawn, allows each pipe organ key to simultaneously play what may be considered a chord of notes consisting of a note plus one or more additional notes higher in the scale. The relationship between the notes in the chord remains constant, creating a pitch series. A mixture is a particular type of compound stop in which the pitch series relationship between the notes is maintained only over discrete sections of the keyboard, and the relationships "break back" in pitch separation one or more times along the keyboard as the musical scale ascends.
The breaks keep the pitch relationship such that a lively timbre is maintained in the produced notes over the entire scale. Without the breaks, the notes at the high end of the keyboard would be compounded with chord notes approaching or exceeding the maximum audible range of the human ear. As frequencies approach the upper limit of the audible range, they sound progressively weaker and eventually become sub-audible. The result is that the warm mixture effect is lost. By breaking back to a lower frequency series relationship as the scale ascends, a good mixture effect can be maintained.
There are a wide variety of recognized and named mixtures in the pipe organ art. Moreover, an organ maker is free to create his own unique mixtures. Selecting a typical mixture, the three rank Fourniture as an example, the correspondence between keyboard regions and the pitches of the desired tones in the mixture as played on a pipe organ are indicated in Table 1 below:
TABLE 1 ______________________________________ Keyboard Rank Rank Rank Note Region I II III Pattern ______________________________________ CC to BB (Base) 22** 26 29 CGC -C to B (Tenor) 19 22 26 GCG C.sup.1 * to B.sup.1 (Middle) 15 19 22 CGC C.sup.2 to B.sup.2 (Treble) 12 15 19 GCG C.sup.3 to C.sup.4 (High) 8 12 15 CGC ______________________________________ *Middle C **Stop-pitch number
The compound stop for the three rank Fourniture mixture outlined above sounds a specific pattern of notes. Within any of the five keyboard regions, a depressed key will sound selected notes which are a specific number of harmonics above that depressed key. For example, the middle C key sounds the number 15, 19 and 22 stop pitches (fourth, sixth and eighth harmonic series) to produce a C3G3C4 mixture note pattern. The number series of the harmonics which are sounded by the three rank Fourniture mixture for each keyboard region are set forth in Table 2 below:
TABLE 2 ______________________________________ Keyboard Rank Rank Rank Region I II III ______________________________________ Bass eighth twelfth sixteenth Tenor sixth eighth twelfth Middle fourth sixth eighth Treble third fourth sixth High second third fourth ______________________________________
In the electronic organ field, various schemes have been proposed for the production of mixtures. One scheme involves substituting, for each organ pipe, an electronic tone source of equivalent pitch and intensity. This approach is straightforward but is relatively expensive and does not lend itself towards the economies of variety which should be provided by an electronic organ.
Another scheme that has been proposed is to "unify" or borrow pitches through various wiring arrangements. In such a scheme, a single electronic tone source may be employed by a plurality of keys on the keyboard. In this scheme, however, "missing notes" may appear when contrapuntal music is played, thereby damaging the continuum of the music.
A further method of producing mixture is possible in a digital electronic organ of the type wherein sample points of complex wave forms are stored as binary numbers in a memory and are read out at the note frequencies. A digital organ of this type is shown in U.S. Pat. Nos. 3,515,792 and 3,610,799. This further method entails programming into the voice memory a complex wave form which is a composite wave form made up of a voice and certain mixture series related harmonics of the voice in order to simulate the desired composite mixture tone. Breaks can be produced by using different composite complex wave forms for different ascending portions of the keyboard. However, by this approach the higher harmonic content of the composite mixture wave forms require a substantial increase in the number of sample points necessary to represent those wave forms, with a concommitant increase in the memory size necessary to accommodate the increased data. Also, the memory must have a different composite wave form for each keyboard region.
Also, in the solution suggested in the immediately preceding paragraph the composite complex wave form is read out of memory at the fundamental note frequency which corresponds to an active key. Thus, the harmonic content of a mixture is present in the composite complex wave form but all harmonics are read out of memory at the rate of the fundamental note frequency. The result is an unnatural slowness of speech or attack for the higher harmonic components of the mixture, rather than the expected brillance associated with a true mixture. This results because the human ear expects a fast attack with a high pitched note or notes. Because the mixture wave form is read out of memory at the single frequency associated with the depressed key, the listener discerns the mixture to be slower in attack than normally expected.
Accordingly, it is an object of the present invention to provide a mixture system in a digital electronic organ or any other similar digital electronic musical instrument in which a mixture pattern having proper speech results. It is a further object to accomplish the above without increasing memory size to accommodate many sample points.